The present invention relates to a sputtering target with low generation of particles, and to the surface processing method thereof.
The sputtering method is a well-known technique as a means for forming a thin film. The basic principle thereof is to apply voltage, in lean gas such as argon, between a substrate (anode side) on which the thin film is formed and a target (cathode side) which is formed from a film-forming substance and placed opposite the substrate at a close distance, so as to change argon gas into a plasma. As a result, the argon ions generated thereby collide with the target, which is a cathode material, the energy thereof discharges (knocks off) the target material outside, and the discharged material is laminated on the opposed substrate surface.
A thin film forming device employing this sputtering principle includes various modified types such as a bipolar bias sputtering device, high-frequency sputtering device, and plasma sputtering device, but all of these devices employ the same basic principle.
The material for forming the thin film is referred to as a target, since it becomes the target for the argon ions. Since sputtering results from the energy of ion collision, the thin film forming material constituting the target is laminated on the substrate in an atomic state, or a cluster state in which the atoms assemble. As a result, a fine and precise thin film can be formed, and this is the reason it is being widely used in various electronic components today.
Recently, this sputtering used for forming thin films is being demanded of extremely sophisticated deposition methods, and an important task is to form films with few defects.
The generation of such defects in this sputtering is not only attributable to the sputtering method, but is also often caused by the target itself. As a cause of such defect generation arisen from the target, there is the generation of particles and nodules.
Under normal conditions, the materials sputtered (discharged) from the target will adhere to the opposed substrate, but the materials are not necessarily sputtered perpendicularly, and are discharged in various directions. This kind of discharged material will adhere to the components inside the sputtering device other than the substrate, and at some point, this will peel off, float, and reattach to the substrate.
This kind of material is referred to as particles, and this is not an originally scheduled thin film forming material. Further, since such particles often adhere as a large cluster, for instance, these particles will cause a short circuit in the fine wiring film for electronic components, and lead to the generation of defective products. It has been discovered that the generation of such particles is due to discharged materials from the target and will increase or decrease according to the surface condition of the target.
Further, generally speaking, materials of the target face do not decrease (erode) evenly due to the sputtering, and the tendency is that a specific area, in a ring shape for example, is eroded according the inherent characteristics of the constituent material and sputtering device, way of applying voltage, and so on. Moreover, depending on the type of target material or the manufacturing method of the target, protrusive substances with numerous bumps known as nodules may be formed on the target.
Since this is one of the thin film forming materials, it will not directly affect the thin film. Nevertheless, minute arcs (microarcing) will occur to the protrusions of the nodules, and it has been observed that this results in the increase of particles.
Further, when numerous nodules are generated, the sputtering rate will change (become delayed), and it will not be possible to control the deposition. At times, these rough and large nodules may peel off and adhere to the substrate.
In such a case, the nodules themselves will become a significant obstacle. Thus, it is sometimes necessary to temporarily stop the sputtering process to remove the nodules. This results in a problem of deteriorating the operation efficiency.
Recently, a target is not formed from a uniform material, and is often used in a state where intermetallic compounds, oxides, carbides, carbonitrides and other substances are mixed in a ductile matrix phase. Here, there is a problem in that the generation of nodules and particles will increase.
As conventional technology, disclosed is a sputtering target in which the processing defect layer (fracture layer) containing minute cracks and defective parts arising during the machine work is removed from the surface of a sputtering target for high-melting-point metal alloy (c.f. Patent Document 1); and a technique for uniformizing the film and inhibiting the generation of nodules and particles by adjusting the surface roughness of the sputtering target so as to reduce the amount of residual contamination, hydrogen content on the surface, and thickness of the affected layer (c.f. Patent Document 2).
Nevertheless, according to these Documents, although it is anticipated that the generation of nodules and particles considerably affects the surface condition of the target, the actual situation is that they are unable to resolve the foregoing problems.
[Patent Document 1]
Japanese Laid-Open Patent Publication No. H3-257158
[Patent Document 2]
Japanese Laid-Open Patent Publication No. H11-1766